Abstract Researches in gender studies shows that children´s play are often sex segregated. This difference is visible when they are about 3 three years old. The research question, in this thesis, is divided into three parts: 1. Are sex differences or sex segregation in children´s play? 2. In what way does it appear in children´s play? 3. What kind of effects do the society and socialization have on children´s identity concerning their role regarding gender? Key findings were that the play is inherent to children and essential for their natural intellectual development and when children play it gives them joy and frolic that is important for them to get an outlet for their activities and creativity.The researches and articles conclusion show large gender segregation characterized by different choice of children’s play, and furthermore, friendships that children form with each other also characterized that children choose their playmate of the same sex. Girls and boys often play different types of plays, the girls´ plays tend to be more organized role plays and they choose more often to play with dolls, and household tools. Boys choose more often to play more frolic-full plays like football or gun play. Children often engage in role plays and pretend plays that are very important for them to learn to adapt to the community that they live in. The community and the socialization starts this gender difference immediately after a child is born by separating them by colours and different types of toys. In children´s play they learn the rules and norms which are prevalent in the society. It is not strange, regarding this, that the development has been in that way that the sexes prefer to play with children of the same sex. It is not the children themselves which shaped this course, rather the society which they live in.